None.
The present invention is related to an improved magnetic microactuator for disc drives having integrated head connections and limiters.
Disc drive systems are well-known in the art and comprise several discs, each disc having concentric data tracks for storing data. The discs are mounted on a spindle motor, which causes the discs to spin. As the discs are spinning, a slider suspended from an actuator arm xe2x80x9cfliesxe2x80x9d a small distance above the disc surface. The slider carries a transducing head for reading from or writing to a data track on the disc.
In addition to the actuator arm, the slide suspension comprises a bearing about which the actuator arm pivots. A large scale actuator motor, such as a voice coil motor (VCM) is used to move the actuator arm over the surface of the disc. When actuated by the VCM, the slider can be moved from an inner diameter to an outer diameter of the disc along an arch until the slider is positioned above a desired data track on the disc. Called tracking, this method of positioning the slider above the desired track on the disc allows the transducing head on the slider to either read from or write data to a selected track on the disc.
The areal recording density of the disc is typically given in tracks per inch (TPI), which is an indication of the number of tracks per inch along the radius of the disc. There is constant pressure to increase the areal density of discs, and thus increase the number of tracks per inch on the disc. As the tracks per inch increase, the accuracy of the system used to position the transducing head above the desired track on the disc must increase in proportion. In an attempt to improve the tracking ability of the slider, secondary microactuators have been placed between the suspension and the slider.
One such microactuator comprises a stationary portion, or stator, as well as a movable portion, or rotor. The rotor is connected to the stator by compliant springs, which allow the rotor to be movable relative to the stator. To move the rotor, the microactuator comprises a motor system, such as a magnetic circuit having either a moving coil or moving magnet portion.
These current microactuator designs are limited in seek performance because the mass-spring resonant mode of the silicon springs connecting the stator and rotor is excited by the primary VCM during seeking. More specifically, as seek accelerations increase beyond 100 G""s, the microactuator motor cannot create enough force to control the rotor position during seek operations. Further, high seek accelerations induce large amplitude ringing of the rotor at the mass spring mode (typically 1,000-3,000 Hz), which unacceptably increases the required settling time. In extreme cases, the rotor may contact the stator at significant velocity. This contact may cause silicon chipping, which creates particles that may cause a catastrophic failure in a disc drive. The contact may also cause silicon cracking, which may eventually lead to the failure of the microactuator device.
In addition to problems associated with increased seek acceleration, there remain challenges to manufacturing microactuators. Currently, the slider is attached to the microactuator using a flex on suspension (FOS) or flex circuit. When connecting the flex circuit to the slider, the relatively large size of the flex circuit results in a fairly coarsely positioned slider. In addition, these mechanical connections have an effect on the stiffness of the microactuator. As a result, it is possible the slider will be positioned on the microactuator having a mechanical bias of as many as 10 microns or more. Previously, this mechanical bias caused by the connection of the head to the flex on suspension was not a problem because the stroke size of the rotor relative to the stator was large enough to accommodate some mechanical bias. Further, the control system of the microactuator could be used to compensate for any such mechanical bias. However, as seek accelerations increase and settling times decrease, it is desirable to limit the stroke size of the microactuator. As a result, any manufacturing processing which results in a mechanical bias when attaching the slider to the microactuator becomes unacceptable.
Thus, there is a need in the art for a microactuator having a decreased stroke size, increased robustness during use at high seek accelerations, and resistance to breakage caused by physical contact between the rotor and stator. Furthermore, there is a need in the art for such a microactuator which is easy to manufacture using existing manufacturing methods.
The present invention is a microactuator design and fabrication method for an improved magnetic microactuator that incorporates mechanical stroke limiters and integrated connections between the flex on suspension and slider bond pads. The stroke limiters (also referred to as seek bumpers) and integrated connections enable low power, mechanically robust operation of the microactuator during high acceleration seek operations. In addition, the present invention allows improved head gimbal assembly (HGA) yield due to the integrated head connections formed on the microactuator. Furthermore, the embodiment allows for integrated piezoresistive position sensors.
The microactuator comprises a stator, a rotor carrying a slider, the rotor being movable with respect to the stator, and a seek bumper system comprising a pliable material located on the stator and the rotor at a location where the rotor contacts the stator during seek operations. The seek bumpers limit silicon-on-silicon contact and reduce the risk of chipping or cracking. In addition to the seek bumpers, the gap between the rotor and stator is made smaller. With a smaller gap, the rotor deflection due to the VCM seek acceleration can be reduced so that the deflection times the spring constant is less than the force available from the microactuator.
To allow for a smaller gap, and to remove mechanical biases, the microactuator is formed having integrated head connections by using buried and surface wires formed on the rotor and the stator. In this way, the connections from the rotor to the head can be made directly, while the connections from the microactuator to the flex circuit can be made at the stator. This allows the desired gap width between the stator and rotor to be sufficiently small, while also removing any flex bias which would result in inadequate space between the rotor and the stator.